Yup, all BT variants released at the same time (i.e. BT-01 Smokescreen, BT-07 Smokescreen GT, BT-08 Meister and BT-15 Prowl) were released in an equal ratio of 3:3 in cases of 6. Only the two versions of BT-06 Tracks shipped independently of each other (since the blue version came out later than the yellow one).

If any variant became rarer than the other, it's because of higher demand, not because it was produced in lower numbers.